For many years, tire curing presses have employed automatic loading mechanisms which typically pick up an uncured or green tire from a loading stand in front of the press and then position the tire in the press for subsequent press closure and cure of the tire. One well-known type of press sold under the trademark AUTOFORM by NRM Corporation of Akron, Ohio features a loading mechanism which is mounted on a vertically and laterally movable press head, or in case the press head tilts, on one or more fixed stanchions in front of the press. During or following movement of the press head between closed and open positions, the loading mechanism is aligned with the loading stand and lower mold half in such positions, respectively.
The loading mechanism has typically comprised a horizontal elevator frame which supports two laterally spaced tire chucks in the case of a dual cavity press. The horizontal frame rides on side tracks fixed to the press head or stanchions and is independently vertically movable by a reversible drive through a loader drive shaft and sprocket chains trained about drive sprockets on the drive shaft and an idler sprocket and connected at respective opposite ends of the horizontal frame. Rotation of the drive shaft in opposite directions moves the horizontal frame up and down.
If one of the drive chains or associated hardware should fail, continued safe operation of the loader mechanism may be jeopardized. Such failure may result in damage to the loading mechanism and/or press if further operations are not immediately ceased. Most prior art safety devices are connected to the mid-point of the frame and focus on keeping the frame from falling in the event of failure. Even with such devices continued operation of the loader drive and/or press even briefly may result in extensive damage to the mechanisms involved.
One attempt to ensure safe operation of a loading mechanism similar to that just described is disclosed in U.S. Pat. No. 4,319,869. The loader safety device of this patent employs a chain anchored at one end to the loader frame and at its other end to the mid-point of the horizontal elevator frame. Such chain is operatively engaged by a sprocket journaled on a carriage which is laterally positioned by a fluid actuator to raise and lower the horizontal frame. In essence, such device apparently serves to overcompensate for the dead weight of the vertically movable loader components which are vertically positioned by a reversible drive through drive chains at opposite ends of the horizontal frame. By reason of such overcompensation, failure of the drive chains or drive will result in upward travel of the horizontal frame to its uppermost extent of travel.